1. Field of the Invention
This invention relates to a magnetic recording and reproduction method, a recording apparatus, a reproduction apparatus and a magnetic recording medium. A plurality of tracks are recorded on the magnetic recording medium by one or a plurality of recording heads, and signals are reproduced from the tracks by one or a plurality of reproduction heads.
2. Description of the Related Art
In recent years, it has been and is being demanded for a magnetic head to achieve higher density recording in order to increase the capacity of magnetic recording media, and a magnetic head suitable to decrease the width of tracks (such decrease is hereinafter referred to as “narrowing”) has been and is being adopted. Generally, to narrowing of tracks, it is a key to enhance the accuracy in tracking servo.
As a countermeasure against the difficulty in servoing which increases as the narrowing of tracks proceeds, a non-tracking system has been proposed for and placed into practical use in magnetic tape recording and reproduction apparatus. The non-tracking system is disclosed, for example, in Japanese Patent No. 1,842,057, Japanese Patent No. 1,842,058, Japanese Patent No. 1,842,059, Japanese Patent Laid-open No. Hei 04-370580, and Japanese Patent Laid-open No. Hei 05-020788. According to the non-tracking system, data are recorded separately in blocks for identification on tracks for which double azimuth recording is performed by helical scanning so that the data can be re-constructed even if an object track is difficult to be reproduced by one tracing operation. By the non-tracking system, a margin four times or more of that for track control within one track necessary for tracking servoing in the past is permitted.
Further, the application of the non-tracking system is not limited to helical scanning, but the possibility that the non-tracking system may be used in linear recording is examined as disclosed, for example, in Japanese Patent Laid-open No. Hei 10-283620 or Japanese Patent Laid-open No. 2003-132504.
Incidentally, where a nonmagnetic support member having stretchability such as, for example, a polyester film is used for a substrate of a magnetic recording medium, even if double azimuth recording is performed, the permissible deformation amount is, for example, up to approximately twice the track width using tracking servoing. If a greater amount of deformation occurs, then a signal is difficult to be reproduced with a sufficiently high S/N ratio. On the other hand, in recording which does not have double azimuths, the width of a guard band which does not extend across tracks is necessary to be suppressed to an amount smaller than the deformation amount of the tape in order that the reliability such as the error rate may not be deteriorated even where tracking servoing is used together.
Such problems as described above arises, in signal reproduction systems which have been implemented heretofore, from significant deterioration of the signal quality by reading a signal from a plurality of tracks at the same time by at least one reproduction head. Further, in order to eliminate this, it has been devised to use a guard band or perform double azimuth recording and to cause a reproduction head to pick up a signal from one track.
However, if it is intended to achieve still higher track density, then the provision of a guard band makes an obstacle. Meanwhile, the double azimuth recording which can reduce interference from an adjacent track upon reproduction decreases the effect of narrowing when such narrowing is implemented.
This similarly applies also to the non-tracking system. In particular, although a reproduction head apparently reproduces a signal across a plurality of tracks, where timing division is applied, the signal is reproduced normally from one track, but reproduction of a plurality of tracks at the same time is not performed.
Further, where it is tried to use the non-tracking system to achieve higher track density, a signal from an adjacent track to an object track is picked up and makes noise. Therefore, the non-tracking system approaches a limit to narrowing of tracks.
As a technique in the past for a magnetic head apparatus other than those described above, a plurality of heads are disposed in one block and a plurality of data frames are recorded at a time as a system for the formation in blocks of the same azimuth in order to enhance the recording density. One of such apparatus is disclosed, for example, In Japanese Patent Laid-open No. 2003-338012 or Japanese Patent Laid-open No. 2004-071014.
In the known apparatus, since the reproduction head width is necessary to be reduced to approximately one half the width of tracks, there is a restriction that a high output of a reproduction signal is difficult to be obtained. This is disadvantageous, for example, in terms of assurance of an SN ratio. Therefore, the apparatus are not necessarily suitable for further higher density recording.
A MIMO (Multi-Input/Multi-Output) technique is known widely as a technique used for radio communication and disclosed, for example, in Japanese Patent No. 3664993.
Also a technique which uses a technique relating to the MIMO for magnetic recording is known and disclosed, for example, in IEEE Trans. Mag. Vol. 30, No. 6, Nov. 1994, p. 5100. However, a subject which appears when it is tried to place the technique into practical use such as, for example, when a reproduction head of a width greater than the width of a recorded track is not solved by the technique, has not been solved by the technique.
The invention of the present application discloses technical contents which have not been foreseen from the arts in the past when it is tried to implement practical use of the MIMO technique for a magnetic recording and reproduction apparatus, which has not been implemented by the technique of the document mentioned in the preceding paragraph as a magnetic recording method which uses the MIMO.